The present invention relates to a process for preforming containers or cartons from a tube formed of a material which can be automatically welded by pressure and containing a liquid, according to which process the filled tube is lowered between two endless series or trains of opposite half-moulds which are caused to descend simultaneously onto the tube for successively gripping the latter. The tube is subjected to the compression of welding jaws for welding it transversely during the descending movement of the half-moulds, after which the preformed container or carton is separated and the two half-moulds are spaced apart from one another.
One process of this type is known, according to which the containers are welded and separated from the tube individually by a single pair of jaws and a cutting means.
Until now, this process does not permit a container production rate which is satisfactory.
It has been found that it would be of interest to increase the rate of production in a same flow production.
It has also been established that it has not so far been possible during manufacture to adjust the volume of the containers when the volume thereof had already been chosen.
The object of the present invention is to overcome these disadvantages
With the container-preforming process according to the invention, the containers of the tube are first welded in sections corresponding to two preformed containers by a pair of upper jaws and then welded individually by a pair of lower jaws.
It is possible by this process to double the speed of descent of the tube between the half-moulds, and as a result to double the rate of production of the containers or cartons, thereby making possible production rates of the order of 5,000 containers per hour.
In accordance with one feature of the invention, the walls of the tube filled with liquid are pressed against the angular walls of the half-moulds while the tube descends into the first lower angular part of the half-moulds at a speed which is slightly greater than the speed of descent of the half-moulds and then descends at a speed substantially equal to that of the half-moulds in the straight section thereof, in order then once again to descend at a speed slightly higher than the speed of the half-moulds in the upper angular part thereof.
According to one embodiment of the invention, the speed of descent of the tube is regulated in relation to the speed of descent of the half-moulds by acting periodically on the spacing between the walls of the tube situated above the half-moulds, as a function of the height of the latter.
Thus, the walls of the tube are tightly applied to the walls of the half-moulds so as to be adapted with force to the shape of the latter, in order to obtain a volume which corresponds to the volume determined by the half-moulds.
According to another feature, the volume of the containers is adjusted by regulating the spacing of the opposite half-moulds.
The present invention also has for its object a means for continuously carrying out the process of preforming containers of different volumes, and for adjusting these volumes.
According to the invention, the means comprise a second pair of welding jaws constantly disposed beneath the first pair and controlled in synchronism with the first pair. The second pair of jaws acts on a section of the tube which was welded top and bottom by the first pair of jaws, in order to provide an intermediate weld.